Not Applicable.
Not Applicable.
1. Field of Invention
The present invention relates generally to microwave devices and, more particularly, to microwave devices having transmission lines connected to a first surface of a substrate and a microwave circuit chip connected to a second surface of the substrate.
2. Description of the Background
In the microwave industry, active microwave circuits, such as monolithic microwave integrated circuits (MMICs), are typically electrically connected to a substrate having peripheral circuitry according to traditional interconnect approaches using wire bonding. The performance of such traditional interconnect approaches, however, is often unacceptable for higher frequency applications, such as above 2 GHz. For example, current wire bonding technology prevents wire bonds from being formed which are less than about ten mils. This drawback, coupled with the fact that wire bonds cannot be formed with acceptably tight tolerances at such dimensions, often results in unpredictable and/or unacceptable transmission characteristics for the resulting microwave devices. In addition, traditional interconnect approaches are highly labor intensive, thus minimizing high volume productivity and associated economies of scale benefits.
In view of these drawbacks, some microwave device manufacturers have mounted microwave circuits using flip chip technology. Flip chip mounting has found wide application in the semiconductor packaging and assembly industry for digital and low frequency analog chips because it typically provides a cost and size reduction for the resulting semiconductor package. In contrast to the conventional wire bonding interconnect approach, the flip chip mounting technique involves flipping the chip and connecting the chip""s top surface to the substrate. A number electrically conductive flip chip bumps, depending upon the complexity of the chip, are typically provided between the chip""s top surface and the substrate to provide an electrical connection between the chip and the substrate, and hence the other components connected to the top surface of the substrate.
In the microwave industry, however, because of difficulties in matching the orientation of the transmission mode fields for the circuits and the substrate, efforts to incorporate flip chip mounting have been primarily limited to devices employing co-planar waveguide (CPW) structures as the transmission media. That is, the circuit and substrate are both designed to support CPW. Many, if not most, commercially available MMICs, however, are designed for microstrip transmission modes, and are therefore ill-suited for CPW transmission structures. Accordingly, using the flip chip technology for microwave devices has ordinarily necessitated redesign or modification of existing microwave circuits to make them compatible for CPW. In addition, the CPW structure has the additional drawback that it still typically requires the use of wire bonding to balance the ground strips of the CPW transmission line structure.
Incorporating flip chip mounting for microwave devices additionally provides disadvantages with respect to thermal handling, especially for power devices. Numerous thermal flip chip bumps must ordinarily be provided between the chip and the substrate to provide a manner for dissipating heat from the chip. The use of the additional thermal flip chip bumps, however, also ordinarily requires a redesign or modification of existing microwave circuits to accommodate the additional bumps. Furthermore, the use of the additional thermal bumps has associated cost, performance, and production drawbacks.
In addition, when using either a traditional interconnect approach or flip chip mounting, external packaging is commonly required to provide electromagnetic and environmental protection for the microwave circuit. Consequently, additional processing steps are required, thereby incurring associated processing costs.
Accordingly, there exists a need for a microwave device in which the microwave circuit is interconnected to the substrate in such a manner as to be acceptable for microwave frequency applications and which does not require the redesign of microwave circuits to accommodate unpopular microwave transmission structures. There further exists a need for a microwave device which provides reliable and efficient thermal handling. There further exists a need for microwave device which does not require additional packaging to provide electromagnetic and environmental protection for the microwave circuit.
The present invention is directed to a microwave device. According to one embodiment, the microwave device includes a substrate having a first surface and a second surface, a plurality of electrically conductive vias extending through the substrate from the first surface to the second surface, a first interconnect trace connected to the first surface of the substrate and electrically connected to a first of the plurality of vias, a second interconnect trace connected to the first surface of the substrate and electrically connected to a second of the plurality of vias, and a microwave circuit chip connected to the second surface of the substrate and electrically connected to the first and second conductive vias. The microwave device may further include a ground plate connected to the second surface of the substrate, wherein the ground plate includes a recessed portion in which the microwave circuit chip is disposed.
The microwave device of the present invention provides an advantage over prior art microwave devices in that it provides a manner for interconnecting most existing microwave circuits, including microstrip-based MMICs, and a substrate without wire bonding or modification of the circuit. The microwave device of the present invention further provides for efficient and reliable thermal handling. The present invention provides the further advantage that the microwave devices are more reproducible and consistent, thus reducing tuning requirements and providing enhanced yield and improved performance. Another advantage of the present invention is that the assembly technique itself provides packaging of the microwave chip, thus obviating the need for additional packaging. Moreover, when used, for example, in constructing a subsystem module, the present invention obviates the need to obtain pre-packaged chips because the chips are packaged as part of the assembly process, thereby reducing the cost and size of the module. These and other benefits of the present invention will be apparent from the detailed description hereinbelow.